The present invention relates to a method and apparatus for monitoring machine parts by measuring the occurring vibrations.
In order to be able to properly operate numerically controlled machines, it is necessary to monitor the machine as it is subject to wear and tear. A monitoring method and the apparatus suitable for this purpose for components of an automatically operating machine must thus be able to detect gradually and/or suddenly occurring changes in the machine state and must switch off the machine, for example, when there is the danger of breakage.
Federal Republic of Germany DE-OS No. 2,557,428, corresponding to U.S. Pat. No. 4,087,801, for example, discloses a device for determining damage at cutting tools in which a detector furnishes an electrical signal corresponding to the vibrations generated at the tool table or in the tool carrier during the cutting process. If, for example, the cutting tool is damaged, the detector produces a high amplitude output signal which is different from the previously furnished signal that was proportional to the acceleration of the mechanical vibration. As a result, the cutting tool is separated from the workpiece so that the anomalous vibration ceases and the detector output drops to a lower level. The drawback here is that the monitoring device reacts only if the damage has already occurred so that considerable damage may occur at the tools or workpieces.
Federal Republic of Germany DE-OS No. 3,408,492 discloses a noise measuring device for measuring anomalous noise in drive mechanisms. By means of a microphone, the device records the noise generated by the drive mechanism being examined, and an adjustable bandpass filter connected to the microphone automatically filters out all components of the microphone output signal except those which have a desired frequency that is a function of the velocity or rpm of the drive mechanism being examined. The data recorded graphically by an X-Y plotter must be evaluated to determine the quality of the drive mechanism being examined. This device thus permits only precautionary tests of drive mechanisms. Since the anomalous noises are a sequence of vibrations emitted previously by the machine, this method is also insensitive.
The other known machine monitoring systems employing the measurement of vibrations are likewise essentially limited to monitoring bearings and are designed for the operating frequencies of the machine, such as, for example, bearing frequency, number of revolutions, and gear engagement frequencies. Depending on the configuration and dynamic behavior of the machine, it is impossible to detect slight changes at operational components of a machine. Moreover, the prior art methods and devices do not permit differentiation between interfering influences emanating from the machine itself or those from extraneous interference. In any case, the often thus falsified measuring results are insufficient to assure a sufficiently sensitive monitoring process.